This piece summarizes some ideal characteristics of substitute cardiac valves. It analyzes them in terms of the four basic types of presently available substitute cardiac valves. Of the four, the caged-disc prosthesis is the least desirable. Ideally the caged-ball prosthesis might be limited to those ptients with volume lesions, i.e., pure or at least predominant regurgitation, because of the problem of prosthetic disproportion. The tilting-disc has favorable hemodynamic and wear characteristics but long-term anticoagulants are essential as with the caged ball and caged disc type of prosthesis. The porcine xenograft at this time, appears quite favorable but sufficient (greater than 5 years) implantation periods for proper evaluation are just beginning to appear, and, therefore, final judgment must be reserved.